Study Onnitrogen Removal And Electricity Production At A Double-chamber Microbial Fuel Cell

Microbial fuel cells(MFCs)are bioreactors that use microorganisms as catalysts to convert chemical energy to electrical energy directly.In this study,dual chamber MFCs were constructed for simultaneous bioelectricity generation and removal of organic matter and nitrogen substance(e.g.,NO2--N,NO3--Nor NH4+-N)as cathode substrate respectively from synthetic wastewater.The influences of operating parameters(e.g.,the concentration of nitrogen substance,flow rate,external resistance and DO and so on)on the performance of denitrifying microbial fuel cell were investigated.The microbial community assessment on the cathode was quantified through metagenome sequencing.Denaturing gradient gel electrophoresis was used to identify the functional characteristics of the cathode nitrite denitrifying bacteria.The working mechanisms were investigated to achieve biological denitrification and electricity generation.The main results are as follows:(1)The influences of operating parameters on the performance of denitrifying microbial fuel cell were investigated when nitrite was used as the cathode substrate.(1)The performance of denitrifying and generating electricity microbial fuel cell could be promoted with increasing substrate concentration in a certain range.When the NO2--N concentration was 100mg/Lon the cathode,the power density,and TN removal loading rate were the highest at 2.22W/m3,and 0.119kg/(m3·d),respectively.(2)It would be rather desirable for the TN removal and electricity generation of MFC at lower external resistance.Operating an MFC at an external resistance close to its internal resistance allowed to maximize the power generation.(3)Increasing the temperature contributed to improve the performance of MFC,for nitrite as electron acceptor in the cathode,the maximum TN removal rate of 0.126 kg/(m3·d)and the maximum power density of 2.22 A/m3 at 32?,but an over-high temperature could inhibit the activity of denitrifying microorganism.(4)Excessively high cathode coulombic efficiency was caused by the reduction of some NO2-into NH4+.(5)The nitrite may have been oxidized by other electrochemical processes,i.e.,water(not molecular oxygen)participates in the oxidation of nitrite to nitrate.(6)After adding NaN3,the respective maximum power density and current density were 1.00 W/m3 and 25.06 A/m3,which were both lower than previousresults.This phenomenon occurred possibly because the addition of NaN3 decreased the reductase activity of N2 O and caused the accumulation of N2 O.(2)It researched the characteristics of the microbial communities at bio-cathodes when the nitrite as the cathode substrate.(1)In MFC with nitrite as substrate,Proteobacteria(50.39%)and Bacteroidetes(11.94%)were the predominant genus.(2)Thauera,Ignavibacterium and Bacillus are the major bacterial genera involved in cathode nitrite denitrification.(3)The performance of microbial fuel cell were investigated when nitrate,nitrite and a mixture of nitrate and nitrite were used as the cathode substrate,respectively.We infer that the nitrite and nitrate removals depended on the electron flow.Power was produced in both tests and minor differences were found with respect to current and power densities.However,regarding nitrogen removal rates,the two experiments differed considerably for removal efficiencies and nitrogen compound dynamics.?For the nitrate as the substrate of MFC,the MFC power density reached the maximum(6.46 W/m3).For the nitrite as the substrate of MFC,the TN removal loading ratereached the maximum(0.126kg/(m3·d)).After adding COD in the cathode chamber can reduce the accumulation of NO2-,the TN removal loading rate increases to 0.157 kg/(m3·d),but electric performance severely reduces the production,power density dropped to 0.43 W/m3.This is because of the addition of COD make cathode heterotrophic bacteria multiply,plenty of cathode TN denitrification removal by the electrode.(4)The simultaneous nitrification and denitrification was successfully accomplished in the cathode of the MFC.The influences of different DO concentration on the performance of denitrifying microbial fuel cell were investigated when simultaneous nitrification and denitrification taken place in the cathode of MFC over ammonia nitrogen.The MFC used in this study operated successfully at higher DO(1.87mg/L)levels.the TN removal loading rate reached the maximum(0.074kg/(m3·d)),the MFC power density was 4.44 W/m3.But an over-high DO or an over-high DO could inhibit the activity of denitrifying microorganism.The TN removal loading rate rate decreased when the DO concentration was higher or lower than 1.87 mg/L.